In recent years, the use of cellular communication systems having mobile terminals which communicate with a hardwired network, such as a local area network (LAN) and a wide area network (WAN), has become widespread. Retail stores and warehouses, for example, may use cellular communications systems to track inventory and replenish stock. The transportation industry may use such systems at large outdoor storage facilities to keep an accurate account of incoming and outgoing shipments. In manufacturing facilities, such systems are useful for tracking parts, completed products, defects, etc.
A typical cellular communication system includes a number of fixed base stations or access points interconnected by a cable medium often referred to as a system backbone. Also included in many cellular communication systems are intermediate base stations which are not directly connected to the system backbone. Intermediate base stations, often referred to as wireless base stations or repeaters, increase the area within which base stations connected to the system backbone can communicate with mobile terminals. Unless otherwise indicated, the term "base station" will hereinafter refer to both base stations hardwired to the network and wireless base stations.
Associated with each base station is a geographic cell. A cell is a geographic area in which a base station has sufficient signal strength to transmit data to and receive data from a mobile terminal with an acceptable error rate. Typically, base stations will be positioned along the backbone such that the combined cell area coverage from each base station provides full coverage of a building or site.
Cellular communication systems such as those described above often involve spread spectrum (SS) technology. An SS communication system is one in which the transmitted frequency spectrum or bandwidth is much wider than absolutely necessary. Generally, SS technology is utilized for communications in the unlicensed bands provided by the FCC for low power communication devices. These bands include the 902-928 MHz and 2.4-2.48 GHz ranges in the U.S. The FCC requires that information transmitted in these bands be spread and coded in order to allow multiple user access to these bands at the same time.
The two most popular spreading methods in spread spectrum systems are referred to as frequency hopping (FH) and direct sequence (DS) spreading. In FH systems, the radio transmitter hops from one carrier frequency channel to another at a specific hopping rate and in a specific sequence that appears to be a random pattern. This pattern is often referred to as a pseudo-random hop sequence. FH systems offer the advantage of high noise avoidance due to the continuous hopping among different frequencies, otherwise referred to as frequency channels. For instance, a noise signal associated with a particular frequency will interfere with a FH modulated waveform only when the FH modulated waveform is sent on a channel which encompasses the frequency of the noise. Since FH systems will typically hop through a large number of channels (e.g., 75 or more), the noise interference will be limited to only every 75 or more hops.
Direct sequence (DS) systems differ from FH systems in that they do not hop among different frequency channels. Rather, DS systems broaden the overall bandwidth of their transmissions by artificially increasing the data bit rate.
More specifically, direct sequence transmissions involve dividing each data bit to be transmitted into a plurality of sub-bits, commonly referred to as "chips". Each data bit is typically divided into ten or more chips, and the apparent data rate and resultant bandwidth are increased proportionally. The process of dividing each data bit into smaller sub-bits is generally referred to as chipping and is based on a predetermined spreading code known as a PN code or PN sequence. Although DS systems do not typically have as high a noise tolerance as FH systems, the DS systems do have advantages related to its ability to transmit data over channels having larger bandwidths. More specifically, the larger bandwidth generally allows for higher rate of data transmissions as compared to FH systems.
Conventional spread spectrum radios typically are configured to handle either frequency hopping or direct sequence communications. FH radios ordinarily cannot communicate with DS radios and vice versa. Moreover, two or more radios which are each DS radios or FH radios cannot necessarily communicate with each other unless they are operating using the same complete set of communication parameters. For example, two DS radios each using different PN codes cannot communicate with one another since neither radio would be able to properly decode incoming signals received from the other radio.
As competition increases among manufacturers of cellular communication equipment, so does the number of different cellular communication systems and radios which are available in the marketplace. Unfortunately, the different systems utilize different FH and/or DS communication parameters resulting in a lack of compatibility among systems. Thus, users of a particular system typically are required to purchase all of their base stations and mobile terminals from the same manufacturer in order to ensure compatibility. Users are unable to shop comparatively from different manufacturers and select those mobile terminals and/or base stations which best suit their needs regardless of the particular system in which they are to be utilized and the specific communication parameters used therein.
Some mobile terminals offer increased versatility by including two or more different radios rather than a single radio. For example, one radio in the mobile terminal is utilized to obtain information from a local area network and another radio is used to transmit this information to a wide area network. Unfortunately, mobile terminals having two or more radios are often more expensive, larger in size, and heavier in weight.
In view of the aforementioned shortcomings associated with conventional radios used in cellular communication systems, there is a strong need in the art for a radio which is compatible with a large number of cellular communication systems. More specifically, there is a strong need in the art for a universal radio which is user adjustable in order to operate in accordance with the communication parameters of different systems. In addition, there is a strong need in the art for a radio which does not require two or more individual radios in order to communicate with other radios in multiple networks.